Prediction of thermal conductivity of micro/nano porous dielectric materials: Theoretical model and impact factors

Abstract

With the stupendous latent of microscale and nanoscale technologies in energy conversion and utilization, the design and analysis of porous dielectric materials with open cells have required a more accurate calculation of the radiative thermal conductivity. This work introduces a mathematical model to accurately calculate the radiative thermal conductivity of micro/nanoscale porous open cell structures. Due to the limitations of the existing radiative thermal conductivity models, a full-scale method based on the Rosseland diffusion equation is proposed. Combining this full-scale Rosseland diffusion equation and fractal thermal conduction methods, the predicted total thermal conductivity values were well matched with the experimental results for various microscale and nanoscale porous open cell dielectric materials, with less than 15% error. Besides, seven influential factors on the thermal conductivity including cell size, porosity, cellular pore shape, volume specific surface area, temperature, refractive index, and extinction index were extensively investigated. The results show that the thermal conductivity of porous open cell materials mainly decreased with an increase in extinction index and/or the porous structure's volume specific surface area but increased with increase in temperature. This certainly indicated the potential of the full-scale Rosseland diffusion method for use in the design of specific micro/nanoscale porous dielectric structures like polymer foam in the personal energy management device or the silica aerogel in radiative cooling system.